Apparatus and method for detecting removal of conveyed work

Abstract

An apparatus comprising a first detector for detecting if conveyed work that has passed or is passing a specific position is or is not present at a first position; a calculator for calculating a distance traveled by the conveyed work based on the specific position; and an evaluator that determines the conveyed work was removed if the first detector does not detect the conveyed work when the conveyed work is determined to be present at the first position based on the calculated traveled distance.

1. An apparatus for conveying work sequentially passed from a first position and second position to at least a specific position, comprising:
 a first detector that detects if the conveyed work is or is not present at the first position; 
 a second detector that detects if the conveyed work that has passed or is passing the first position is or is not present at the second position; 
 a first calculator that calculates a first distance travelled by the conveyed work after the conveyed work is known from a detection result of the first detector to have passed the first position; 
 a second calculator that calculates a second distance travelled by the conveyed work after the conveyed work is known from a detection result of the second detector to have passed the second position; and 
 an evaluator that determines, after the presence of the conveyed work is no longer detected at the second position, if the conveyed work was or was not removed when the conveyed work was present at least at the second position based on the calculated first travelled distance and the calculated second travelled distance. 
 
   
   
     2. The apparatus according to  claim 1 , wherein:
 the first calculator calculates as the first travelled distance the distance the conveyed work moves from when the first detector stops detecting the conveyed work until the leading end of the conveyed work reaches the specific position; 
 the second calculator calculates as the second travelled distance the distance the conveyed work moves from when the second detector stops detecting the conveyed work until the leading end of the conveyed work reaches the specific position; and 
 the evaluator compares the difference of the calculated first travelled distance minus the calculated second travelled distance with the gap between the first position and the second position, and determines that the conveyed work was removed if this difference is less than the gap. 
 
   
   
     3. The apparatus according to  claim 2 , wherein:
 the length of the conveyed work along the transportation direction is shorter than the distance between the second position and the specific position; and 
 the evaluator compares the difference and the gap when the leading end of the conveyed work is expected to reach the specific position. 
 
   
   
     4. The apparatus according to  claim 1 , further comprising:
 a third detector that detects if the conveyed work that has passed or is passing a specific position is or is not present at a third position; 
 a third calculator that calculates a third distance travelled by the conveyed work referenced to the specific position; and 
 a second evaluator that determines that the conveyed work was removed if the third detector does not detect the conveyed work even though the conveyed work is determined present at the third position based on the calculated third travelled distance. 
 
   
   
     5. The apparatus according to  claim 1 , further comprising:
 a third calculator that calculates a third distance travelled by the conveyed work from the specific position; and 
 a second evaluator that determines that the conveyed work was removed if the second detector does not detect the conveyed work even though the conveyed work is determined present at the second position based on the calculated third travelled distance and the length of the conveyed work in the transportation direction. 
 
   
   
     6. The apparatus according to  claim 5 , wherein the length of the conveyed work in the transportation direction is acquired based on detection results from the first detector and the second detector. 
   
   
     7. The apparatus according to  claim 1 , further comprising:
 a second evaluator that determines that the conveyed work was removed if the second detector does not detect the conveyed work even though the conveyed work is determined present at the second position based on the calculated first travelled distance. 
 
   
   
     8. The apparatus according to  claim 1 , wherein:
 the first calculator calculates the distance moved by the conveyed work from when the first detector detects the conveyed work to when the first detector stops detecting the conveyed work as the first travelled distance; 
 the second calculator calculates the distance moved by the conveyed work from when the second detector detects the conveyed work to when the second detector stops detecting the conveyed work as the second travelled distance; and 
 the evaluator determines that the conveyed work was removed if the calculated second travelled distance is shorter than the calculated first travelled distance. 
 
   
   
     9. The apparatus according to  claim 8 , wherein the first detector is located downstream of the second detector in the transportation direction. 
   
   
     10. The apparatus according to  claims 1 , wherein:
 the apparatus is connected to enable communication with a host device; and 
 the evaluator determines if the conveyed work is or is not removed according to a command that is sent from the host device to enable or disable a removal detection function. 
 
   
   
     11. A method of conveying work sequentially passed a first position and second position to at least a specific position, comprising steps of:
 detecting if the conveyed work is or is not present at the first position; 
 detecting if the conveyed work that has passed or is passing the first position is or is not present at the second position; 
 calculating a first distance travelled by the conveyed work when the conveyed work passes or has passed the first position; 
 calculating a second distance travelled by the conveyed work when the conveyed work passes or has passed the second position; and 
 determining if the conveyed work was or was not removed when the conveyed work was present at the second position based on the calculated first travelled distance and the calculated second travelled distance after the presence of the conveyed work is no longer detected at the second position. 
 
   
   
     12. A method comprising steps of:
 detecting if a conveyed work that was conveyed to a specific position and has passed or is passing the specific position is or is not present at a target position; 
 calculating a first travelled distance, which is the distance travelled by the conveyed work from the specific position; and 
 determining that the conveyed work was removed if the conveyed work is not detected when the conveyed work is determined present at the target position based on the calculated first travelled distance. 
 
   
   
     13. The method according to  claim 12 , wherein the specific position is an indexing position of the conveyed work, and the target position is the detection position of a discharge detector that detects discharging the conveyed work. 
   
   
     14. The method according to  claim 12 , wherein the specific position and the target position are the detection position of a bottom-of-form detector that detects the trailing end of the conveyed work.